Method of writing, erasing, and controlling memory for memory device

Abstract

Data transferred from a host computer to a memory device is written into sectors whose addresses in a memory area are decoded by a decode table. Old data to be updated by the above data is erased or marked with erase flags. At a predetermined point of time, in order to create free areas, necessary data is evacuated to a primary memory media and unnecessary data indicated by erase flags is erased by a unit of predetermined memory size. Part of the memory media which has become defective is marked with a defect flag, and is replaced by an alternate area. In doing so, the decode table is rewritten to arrange the memory area.

What is claimed:  
     
       1. A method of writing and erasing data in a memory device with a memory area having a plurality of blocks each with a plurality of sectors, the memory device erasing data by the unit of one block, the method comprising: 
       selecting a first predetermined number of blocks from a top of a first list in which the blocks are ranked in a descending order of a number of necessary sectors in each of the blocks;  
       selecting a second predetermined number of blocks from a top of a second list in which the blocks are ranked in an ascending order of a number of necessary sectors in each of the blocks; and  
       evacuating the necessary sectors from the first predetermined number of blocks and a second predetermined number of blocks to other blocks which have free sectors.  
     
     
       2. The method as claimed in  claim 1 , wherein said evacuating the necessary sectors distributes the necessary sectors to the other blocks by mixing the necessary sectors from the first predetermined number of blocks and the necessary sectors from the second predetermined number of blocks. 
     
     
       3. The method as claimed in  claim 1 , wherein said evacuating the necessary sectors distributes the necessary sectors to the other blocks evenly. 
     
     
       4. The method as claimed in  claim 2 , wherein said evacuating the necessary sectors distributes the necessary sectors to the other blocks evenly.